Method and compositions for the control of coccidiosis in poultry

ABSTRACT

Aqueous concentrates intended for addition to nutrient material in the manufacture of feedstuffs for poultry are provided consisting essentially of water and from about 1000 to about 1,000,000 viable sporulated oocysts of at least one species of coccidia to which poultry are susceptible and at least one edible thickening agent which facilitates the mixing of the oocysts into feedstuff without destructive frictional heat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of pending application Ser. No. 751,276filed on July 2, 1985, now U.S. Pat. No. 4,752,475 which is a divisionof application Ser. No. 487,593 filed on Apr. 27, 1983, now U.S. Pat.No. 4,544,548 which is a division of application Ser. No. 339,311 filedon Jan. 15, 1982. Application Ser. No. 339,311 is a division ofapplication Ser. No. 228,479 filed on Jan. 26, 1981, which was acontinuation of application Ser. No. 049,070 filed on June 18, 1979,which itself was a continuation of application Ser. No. 959,984 filed onNov. 13, 1978, of which the last four applications listed above are nowabandoned.

The present invention relates to methods and compositions for thecontrol of coccidiosis in poultry.

In this specification, the term "poultry" is used to denote birds of theorder Galliformes such as the ordinary domestic fowl or chicken (Gallusdomesticus), turkeys ( Meleagris), pheasants (Phasianus), partridges(Pedrix), grouse (Lagopus), guinea fowl (Numida) and peacocks (Pavo),and also birds of the order Anseriformes such as ducks (Anas) and geese(Anser).

Coccidial infections are encountered in all poultry species that arereared by man. Such infections are particularly troublesome when theyoccur in flocks of birds reared under modern intensive husbandryconditions. Infection can spread rapidly throughout the flock, and atthe very least can cause poor growth. Severe infection can lead to deathof the birds. Thus for many years considerable effort has been expendedin attempts to find reliable prophylactic measures against suchinfections, and in particular to find ways in which birds can beimmunised effectively against the incidence of such infections. Thepractical benefit of any effective immunising technique will be topromote the growth of poultry to which immunity is imparted, at least inthe sense that the negative effects on growth caused by coccidialinfection will be counteracted thereby.

It has already been established that poultry which have survivedinfection by coccidiosis retain some degree of immunity against furtherinfection. This effect has been put to practical use in a proceduredescribed in U.S. Pat. No. 3,147,186 wherein sub-clinical infection isinduced in poultry by the administration of a single oral inoculumcontaining 100-800 viable sporulated coccidia oocysts per bird. Theresulting infection, re-inforced by secondary and tertiary cycles ofinfection caused when the birds pick up further viable sporulatedoocysts resulting from those excreted by infected birds, impartsimmunity to the flock as a whole. The efficiency of this technique isenhanced if an anti-coccidial drug is administered to the poultry at asub-curative level, so reducing the pathogenic effects of the coccidiawhile still permitting the life cycle of the organism to produce furtherviable sporulated oocysts in the litter which can be ingested by othermembers of the flock. An oral liquid inoculum of viable sporulatedcoccidia oocysts for this purpose is available commercially. While thisis undoubtedly an effective technique for imparting immunity to poultry,it requires the poultry farmer to conduct a specific inoculatingprocedure over and above all of the normal tasks that need to beperformed in conventional poultry rearing. Moreover, in unskilled hands,there is the risk that in error a dangerous overdose of oocysts could beadministered to the birds, leading to severe and perhaps fatalinfection. Finally, conditions of temperature and moisture in the littermust be carefully controlled to ensure the sporulation of excretedoocysts necessary to induce the progressive cycles of immunisinginfection. One embodiment of the procedure described in U.S. Pat. No.3,147,186 is the administration of the single oral inoculum of oocystsvia the drinking water or the feedstuff given to the poultry.Nevertheless, neither of these variants overcomes the problems of theadditional task imposed on the poultry farmer or the possible risk ofoverdose, as it still remains the responsibility of the farmer toprepare the inoculated water or feedstuff and to administer it at thecorrect time. A further disadvantage acknowledged in U.S. Pat. No.3,147,186 in relation to administration of the single inoculum via aspecially prepared feedstuff is that it is best to wait until thepoultry have learned to eat before presenting them with the inoculatedfeedstuff. Thus by implication the dangerous post-hatching period duringwhich the chicks have no immunity against coccidial infection could beprolonged unduly through delayed administration of the inoculum.

Thus we believe there is still a need for a method of imparting immunityto poultry which does not impose any additional tasks orresponsibilities on the poultry farmer and which reduces the potentialrisk of overdose.

By the invention it has been found that poultry can be immunisedeffectively against coccidiosis if a low level of viable sporulatedoocysts of one or more coccidia species infective to the species ofpoultry concerned is administered in a feedstuff given to the poultry oncontinuous or at least frequent basis.

Accordingly, the invention firstly provides a method for promoting thegrowth of poultry, in which method the poultry are reared ton a dietcomprising nutrient feed material containing added viable sporulatedoocysts of at least one species of coccidia to which the poultry aresusceptible, the oocysts being present in a concentration sufficientonly to induce sub-clinical infection in the poultry.

To this end, another embodiment of the invention is a commercial poultryfeedstuff comprising nutrient material and containing per kg thereoffrom about 10 to about 10,000 viable sporulated oocysts of at least onecoccidia species to which poultry are susceptible.

By providing the poultry with oocysts in their regular feedstuff, thepoultry are able in effect to conduct a controlled progressiveself-inoculation. Daily intake of oocysts is dictated by the quantity offeedstuff eaten by each bird, and the level of oocysts in the feedstuffcan be regulated by the feedstuff manufacturer whose sophisticatedquality control facilities can more readily ensure that no risk ofoverdose can possible arise. Moreover, by having the oocysts in theirnormal diet, it is possible to ensure that the chicks are consumingappropriate levels of oocysts as soon as they begin to ingest solidfood, and thus the immunising process can begin at a very early momentin their post-hatching life.

Different species of poultry suffer from infections caused by differentcoccidia species. The domestic fowl (Gallus domesticus) can be infectedby any of the coccidia Eimeria tenella, E. necatrix, E. brunetti, E.maxima, E. acervulina and E. praecox. The following coccidia areimplicated in infections of turkeys (Meleagris): Eimeria melagrimitis,E. dispersa, E. meleagridis, E. gallopavonis, E. adenoides, E. innocuaand E. subrotunda. Domestic ducks (Anas) suffer from infections causedby Tyzzeria perniciosa and also, it is believed by Eimeria Anatis whichthey can acquire from wild ducks (Anas platyrhyncos). Geece (Anser) cansuffer from infections caused by Eimeria anseris, E. nocens and E.parvulaand in addition it is believed that domestic geese can pick upinfections from Canada geese caused by Eimeria hermani, E. striata andE. fulva. The other poultry species referred to earlier each suffer frominfections caused by characteristic coccidia, and the invention isequally appropriate and effective in the control of infections caused bythe characteristic coccidia in such other poultry species. All oocystlevels mentioned in this specification should be construed as being pereach coccidia species present.

Preferably the poultry feedstuff of the invention will contain not morethan about 2,500 viable sporulated oocysts per kg. Although positivebenefits will be obtained by the introduction of the sporulated oocystsinto the feedstuff given to an individual bird at any stage of its life,it is preferable that the bird is provided with a feedstuff containingthe low levels of sporulated oocysts as soon as it has been hatched andcommences feeding. As the bird grows, its daily food requirementincreases dramatically. Taking the domestic fowl (Gallus domesticus) asan example, at the "first feeding" stage the chick will consumeapproximately 2 g of feedstuff per day. After 10 days this will haverisen to about 10 g per day, and after 30 days the bird will beconsuming perhaps 80 g per day. The nutritional requirements of the birdchange as it develops, and commercially-available poultry feedstuffs aresold with a range of formulations intended for the different stages ofthe bird's development. Typically such a range will include feedstuffsspecifically formulated for "starters", "growers" and "breeders/layers".In order to ensure that at each stage of its development the bird isconsuming an appropriate number of sporulated coccidia oocysts per day,it may be appropriate for the different feedstuffs to contain differentnumbers of oocysts per kg.

For optimum immunization, we believe that a newly-hatched chick shouldconsume about 1 to 20 viable sporulated oocysts per day. During thefirst 10 days of growth, this level should rise to about 2 to 50 oocystsper day. By day 30, the level of oocysts consumed per day should be ofthe order of about 5 to 200.

Preferably a "starter" feedstuff will contain at least about 500 viablesporulated oocysts per kg. Preferably the maximum level of oocysts willbe about 5,000 per kg, and ideally not more than about 2,000 per kg.

In a "grower" feedstuff the minimum level of viable sporulated oocystsis preferably about 50 per kg. The upper level of oocysts is preferablyabout 2,000 per kg, and ideally not more than about 500 per kg.

In a "breeder/layer" feedstuff an appropriate minimum level of viablesporulated oocysts is about 10 per kg. Preferably the upper level ofoocysts does not exceed about 1,000 per kg, and ideally is not greaterthan about 100 per kg.

The viable sporulated oocysts can be obtained by deliberately infectinga donor flock of birds, and collecting the oocysts from their droppings.Techniques for obtaining viable sporulated coccidia oocysts per se arewell known in the art, and form no part of the present invention. Onesuitable procedure is described at length in U.S. Pat. No. 3,147,186.

The oocysts can be added directly during the mixing of the poultryfeedstuff, or can be added via a pre-mix. Alternatively, a suspension ofthe oocysts, preferably aqueous, can be sprayed onto the poultryfeedstuff. This is particularly useful when a pelleted feedstuff isrequired, because the oocysts must not be applied until all stepsinvolving heat in the manufacture of the of the feedstuff have beencompleted. The oocysts are very easily killed by heat, and a proceduresuch as pelleting would destroy any oocysts present in the pelletedmixture. Due to the heat-sensitivity of the oocysts, a feedstuff of theinvention must not be exposed to any extremes of heat during storage.Moreover, the oocysts are also damaged if they suffer dehydration, andfor this reason the feedstuff should never be allowed to dry outcompletely. Preferably the moisture level in the feedstuff should remainin the range of about 6 to about 12% by weight, although higher moisturelevels can be used where this does not lead to spoilage of the feedstuffby the growth of moulds, etc, during storage.

A further embodiment of the invention is an essentially solidfree-flowing pre-mix comprising viable sporulated coccidia oocystsdistributed in a carrier, which can be added as a dry composition to apoultry feedstuff formulation, or which can be made into a paste orslurry with water for incorporation into a poultry feedstuff byadmixture or by spraying. Preferably the carrier is an edible thickeningagent, such as a colloid-forming material although materials that formgels can also be employed. One suitable thickening agent is a starch,such as potato starch, wheat starch or maize (corn) starch. However,starches suffer from the disadvantage that they are not so readilymixable with water, and can lead to relatively lumpy pastes. A morepreferred thickening agent is a cold water soluble polysaccharide, suchas an alkyl cellulose, a carboxyalkyl cellulose or a hydroxyalkylcellulose. Sodium carboxymethyl cellulose is especially preferred.Alternatively, gums such as locust bean gum, guar gum and gum tragacanthcan be used. If desired, mixtures of any of these thickening agents canbe employed. The number of sporulated oocysts incorporated in thepre-mix will depend on the number required per unit weight of thepoultry feedstuff and the desired or permitted level of the carrier inthe poultry feedstuff. Typically, a pre-mix of the invention willinclude at least 1,000 sporulated oocysts per kg. Preferably thisminimum level will be at least about 5,000 per kg, and ideally at least10,000 per kg. A typical general-purpose pre-mix can contain from about50,000 to about 500,000 sporulated oocysts per kg. A maximum level isnot readily definable: a pre-mix containing in excess of one millionsporulated oocysts per kg could be useful where a high oocysts level inthe feedstuff is needed but where the carrier level must be kept to aminimum. It will be appreciated that pre-mixes of type just describedcan be used also to aid the incorporation of other essential traceingredients into the poultry feedstuff, for example, mineral additiveswhich are important especially in promoting egg-shell formation inlaying birds, vitamins and amino acids such as lysine, and carotenoidpigments commonly used to influence the colour of egg yolks. If desired,one or more of these minor ingredients can be included with the oocyststogether in one composite pre-mix. To maintain the viability of theoocysts, the pre-mix should have a moisture content in the preferredrange of about 6 to about 12% by weight.

Another embodiment of the invention is an aqueous concentrate containingviable sporulated oocysts, intended for addition as such during themanufacture of poultry feedstuffs. Like the essentially solid pre-mixjust described, such an aqueous concentrate can be an article ofcommerce in its own right. Preferably the aqueous concentrate containsthe oocysts in suspension. To this end, it is preferable that theaqueous concentrate also comprises one or more edible thickening agentsof the types just described in relation to the essentially solidpre-mix. The same preferences for cold water soluble polysaccharides ingeneral, and sodium carboxymethylcellulose in particular, apply. In thisinstance, however, only low levels of such materials, sufficient topromote the suspending ability of the aqueous concentrate without soincreasing its viscosity that it becomes unpourable or unsprayable(depending on the desired mode of addition to the poultry feedstuff) arerequired. Very broadly, it can be said that the optimum level for anygiven thickening agent is likely to lie in the range of about 0.1 toabout 10% by weight of the aqueous concentrate, but it will beappreciated that the properties of commercially available thickeningagents vary widely one from another. The levels of oocysts in theaqueous concentrate are governed by the same considerations as thosejust described in relation to the essentially solid pre-mix: thusstrictly comparable levels are appropriate.

An advantage of an aqueous oocysts concentrate containing an ediblethickening agent such as a cold water soluble polysaccharide is that thethickening agent binds water. When the aqueous concentrate is blendedwith dry ingredients in the manufacture of a poultry feedstuff thebinding of the water by the thickening agent prevents rapid absorptionof the water into the feedstuff and thus assists in the spreading of theoocysts uniformly throughout the bulk of the feedstuff. If the water isabsorbed too rapidly, the resulting local concentrations of oocysts maybe difficult to break up by subsequent processing without undue risk ofloss of viability due to frictional heat, for example.

Due to the loss of viability that can result if the sporulated oocystsare allowed to dehydrate, it can be advantageous to encapsulate theoocysts within a relatively water-impervious edible material. Clearlythe encapsulating material should be such that release of the oocystswithin the gut of the bird is effected readily. Optimally theencapsulating material should have a melting point at or slightly belowthe body temperature of the bird, which is typically about 40° C.However, materials of higher melting point can be used so long as theresulting capsule is sufficiently fragile to be crushed in the gizzardof the bird. It will be appreciated that where the encapsulatingmaterial is to be applied in the molten state, the temperature and heattransfer characteristics of the encapsulation procedure must not be suchthat the sensitive oocysts suffer a significant loss of viability due tobeing overheated. In practice it is preferable that the melting point ofthe encapsulating material should be in the range of about 35 to about60° C. Fats and waxes, such as stearine, having melting points withinthis range are particularly suitable. An appropriate encapsulatingtechnique is co-extrusion of the molten encapsulating material around anaqueous suspension of the oocysts, using for example the well-known 3Mprocess. The aqueous suspension preferably comprises the oocysts inphysiological saline or phosphate-buffered saline.

Apart from the inclusion therein of the viable sporulated oocysts, it isnot essential for the composition or physical form of the poultryfeedstuff to be altered in any way in putting the invention into effect.Any of the currently standard "complete" or nutritionally "balanced"commercial poultry feedstuff formulations can be used, and the nutrientmaterial in the feedstuff can thus comprise any of the protein,carbohydrate and fat ingredients normally found in such feedstuffs. Thenature of such standard ingredients, such as the various fish meals,milled grain and other plant material, and mineral additives, and thenutritional requirements such as minimum levels of vitamins, amino acidsand trace elements, are well known in the art and documented in thetechnical literature, and such detail forms no part of the presentinvention.

The treatment and prevention of coccidial infections in poultry usinganti-coccidial drugs is well known. However, in an important preferredsub-feature of the invention we have found that very effective controlof coccidial infections can be achieved if in addition to feeding thepoultry with a feedstuff containing sporulated coccidia oocysts inaccordance with the invention, the poultry are also exposed to one ormore anti-coccidial drugs at a curative level. We have observed thatthis combination of sporulated oocysts in the feed and the additionaladministration of anti-coccidial drug interrupts the life cycle of theparasite and effectively prevents any transmission of infective oocyststhroughout the entire course of immunisation. In this respect thepresent invention represents a further departure from the conceptsdisclosed in U.S. Pat. No. No. 3,147,186, wherein an anti-coccidial drugis used at a sub-curative level merely to reduce the pathogenic effectsof the coccidia without eliminating their ability to produce the viablesporulated oocysts needed to induce further cycles of sub-clinicalimmunising infection. In our invention we prefer the anti-coccidial drugto halt effectively the life cycle of the coccidia, so preventingexcretion of viable oocysts into the environment. Thus, in the idealsituation, the birds would ingest only those oocysts which have beendeliberately added to their diet. Clearly, the anti-coccidial drug usedin accordance with our invention must not be one which halts thecoccidia life cycle at so early a stage that no development takes placein the gut of the bird sufficient to induce an appropriate immuneresponse.

Preferably the anti-coccidial drug used is one in which the majoractivity is directed against parasitic stages of the coccidium appearingon the fourth day of infection of later. Examples of appropriateanti-coccidial drugs are nicarbazin, furazolidone, nitrofurazone,nihydrazone, sulphaquinoxalene, sulphanitran, dinsed, ormetroprim,sulphadimethoxine and ethopabate. The anti-coccidial drug can beincluded as an ingredient of the feedstuff itself, or if preferred itcan be administered separately to the poultry. Standard curative doserates as recommended by the manufacturer of the drug can be employed.

The invention will now be described, by way of example only, withreference to the control of infections in the domestic fowl (Gallusdomesticus) caused by Eimeria tenella, which is one of the leastimmunogenic of all coccidial species, and certainly one of the mostpathogenic and virulent. Any technique that is demonstrably effective inthe control of Eimeria tenella infections will, by implication, be atleast equally effective against the less intractable coccidia.

The accompanying drawings, of which:

FIG. 1 is a graph illustrating the numbers of oocysts ingested andexcreted by birds fed an immunising diet of the invention;

FIG. 2 is a graph comparing the percent weight gain of two groups ofbirds following a severe challenge with viable coccidia oocysts, onegroup of birds having been immunised in accordance with the invention;and

FIG. 3 is a pair of block diagrams illustrating in terms of excretedbloody droppings the symptoms exhibited by the two groups of birds whosepercent weight gain is compared in FIG. 2; are relevant to Example 1.

EXAMPLE 1

(1 ) Management of Birds

Newly hatched Cobb broiler chicks were collected from a commercialhatchery and immediately divided at random into groups of six. Groups inwhich the oocyst output was to be monitored were kept in cages having anopen wire-mesh floor through which their droppings could fall, and thosewhich were intended to demonstrate the efficacy of the oocyst-containingfeedstuff were kept on litter. The accommodation in which all chickswere housed had been thoroughly treated to ensure freedom from residualoocysts.

(2) Oocysts

Oocysts were obtained by infecting 3-week old Cobb broiler chicks by anoral dose of 5,000 oocysts per bird. Their droppings were collected ondays 6, 7 and 8 after infection, mixed with approximately twice theirvolume of 2.5% aqueous potassium dichromate solution and thenhomogenised to give a smooth slurry. The slurry was strained through anylon gauze and the oocysts were recovered from the filtrate by saltfloatation, as follows. Firstly, the oocysts were sedimented bycentrifugation at 1,000×g for 15 minutes and the sediment was thenresuspended in saturated aqueous sodium chloride solution. This wassubjected to centrigugation at 500×g for 10 minutes, and the oocystssuspension which remained was drawn off and diluted with 10 volumes ofdistilled water. Centrifugation at 1,000×g for 15 minutes brought theoocysts down into a pellet. The whole salt floatation procedure wasrepeated, and the resulting oocysts pellet was finally taken up in 2.5%aqueous potassium dichromate. The extracted oocysts were sporulated bycontinuous aeration of this suspension for four days at 28° C. As astock suspension, these oocysts were maintained at 4° C. in phosphatebuffered saline.

(3) Preparation of the oocysts-containing feed

Birds were immunized by a continuous "trickle" of low numbers of oocystsgiven in the feed. They were added at a level of 1,250 per kg. of meal.To ensure even spreading throughout the whole feed and to provide anadditional means of mechanical protection, the oocysts were firstsuspended in a starch paste which was then mixed with the meal in aHobart cutter/mixer bowl. The paste was prepared by making a smooth,thick suspension of 300 g of wheat flour with 1,000 ml of cold water.The paste was steamed for 30 minutes and then cooled before addition ofthe oocysts, at a level of 6,000 per 125 ml of paste. This providedenough material to treat 4,500 g of meal. Birds were fed ad-libatum onthis feed and their oocyst intake was calculated from the amount of feedconsumed. Line A in FIG. 1 gives the number of oocysts consumed by eachbird per day of the experiment up to day 34.

(4) Viability of Oocysts

The viability of the oocysts in the feed was checked at fortnightlyintervals by feeding the diet to fresh susceptible birds and thenmonitoring their oocysts output on days 6-11 after the start of oocystfeeding.

(5) Assessment of Infections

The effects of the immunizing infections were monitored by the dailyrate of oocyst discharge (average per bird), the rate of weight gain andthe presence of blood in the droppings. Line B in FIG. 1 shows theaverage daily oocyst output of each bird consuming the oocyst-containingfeed. Weights were recorded at weekly intervals during the immunizationperiod but more frequently after the challenge. They were expressed asthe percentage weight increase since the start of the immunization orsince the administration of the challenge inocula. Lines C and D in FIG.2 show respectively the average percentage weight gain of the immunizedand control birds after challenge.

When blood was seen in the droppings, a crude assessment was made on thebasis of the number of fresh blood-containing droppings which could beseen. A scoring range of 0-4 was used, from 0 (absent) through 2(frequent) to 4 (uniformly scattered). The results obtained are recordedin FIG. 3.

(6) Continuous in-Feed Immunization

This experiment was designed to establish whether sporulated oocystsadded to the feed in very low numbers could survive and causecontrolled, sub-clinical infections when fed to susceptible birds. Theimmunity arising from this treatment, continued for 34 days, was testedby means of a severe challenge with 500,000 oocysts. Three groups, eachof six birds, were used. The first and second groups received theoocysts-containing diet from one day old and the third received anormal, oocysts-free diet. In order to simulate the least favourableconditions likely to be encountered in commercial situations, groups 1and 3 were kept on deep litter. Group 2 kept on wire so that the dailyoocysts discharge resulting from the oocysts in the diet could easily bemonitored.

(7) Results

The oocysts survived in the feed for the duration of the experiment, asoocysts were passed from day 8 right up to the time that the immunizingdiet was withdrawn, as shown in FIG. 1. Also, when the diet was fed tofresh susceptible birds, large numbers of oocysts were passed on days6-11 following dosing. It was obvious from the pattern of oocystdischarge that a substantial immunity was beginning to develop soonafter the birds reached 3 weeks of age, for a soaring oocyst dischargewas promptly checked and brought under control by day 25, despite thecontinual intake of oocysts at an incrasing rate. Challenge on day 34with 500,000 oocysts produced only a trivial peak of oocyst discharge onday 42.

The immunizing oocysts produced no detectable pathogenic effects,despite the fact that these birds were on litter and could have pickedup numerous fresh oocysts. No bloody droppings were seen throughout thewhole immunizing period but, more importantly, the mean weight gains ofthe control, unimmunized group and the immunized group werestatistically identical up to the day of challenge.

Challenge with 500,000 oocysts on day 34 caused severe disease in thecontrol group as can be seen from the statistically significantdifferences in weight gain and the bloody droppings score shown in FIGS.2 and 3. The immunized group were apparently completely unaffected butthere was no mortality in either group.

(8) Conclusions

The most important conclusions to be drawn from these results are thatoocysts added to the diet in this way survive for at least one month andthat, administered in this form, they can induce a strong immunitywithout causing pathogenic effects. Despite the use of fully virulentorganisms the unique, self-limiting nature of the coccidial life cyclecan be exploited, allowing complete control to be exercised over thelevel of infection and its consequent pathogenicity during the criticalphases of immunization.

Clearly, the fresh oocysts discharge into the litter did not constitutea hazard. The conditions under which the birds were kept were designedto allow the maximum opportunity for re-infection, but because each birdwas receiving a steady dose of oocysts in its feed, an effective, if notsolid, immunity had built up before extensive sporulation could occur.

Because the oocysts were included in the feed they would have been takenin constantly, rather than at daily vaccinating events and the processof vaccination was, in effect, carried out by the birds themselveswithout the need for any additional handling. An inevitable consequenceof this mode of administration would be that the birds would receive asteadily increasing does of oocysts as their food intake increased. Whena bird consumed 10 g of food in one day, then the daily oocyst dosewould have been about 10, increasing to about 50 when the bird's foodconsumption increased to 50 g per day. An equally important feature wasthat once the oocysts had been uniformly distributed throughout themeal, there could be no possibility of an overdose--the bulk of foodwhich would have been necessary to provide a dangerous number of oocystswas excessive.

The control birds were seriously affected by the challenge, but overall,they fared better than expected. This was almost certainly due tofailure to completely exclude oocysts from their environment and, sincethe conditions in which they were kept were not designed to preventinfection, it is possible that they may have acquired some lightresistance.

Nevertheless, by the time the oocyst-containing feed was withdrawn atday 34, the immunized birds were completely in equilibrium with theirenvironment and were capable of withstanding a massive infection ofoocysts.

EXAMPLE 2

An aqueous concentrate was prepared by taking up approximately 6,000viable sporulated Eimeria tenella oocysts, obtained in the mannerdescribed in Example 1, in 100 ml physiological saline (0.85% by weightsodium chloride in water) containing dissolved therein 2.5 g sodiumcarboxymethyl cellulose (Hercules KLUCEL). This concentrate was blendedwith 4,500 g of a standard commercial poultry meal, using a Hobartcutter-mixer the concentrate simply being poured into the bowl of therotating mixer containing the meal, mixing being continued until avisually homogeneous product resulted. Domestic fowl reared fromhatching on this feedstuff exhibited the same good immunity against E.tenella challenge as was exhibited by the immunized chicks of Example 1.

What is claimed is:
 1. An aqueous concentrate, intended to be added tonutrient material in the manufacture of a feedstuff for poultry,consisting essentially of water, from about 1,000 to about 1,000,000viable sporulated oocysts, of at least one species of coccidia to whichpoultry are susceptible, per kilogram of aqueous concentrate, and atleast one edible thickening agent selected from the group consisting ofstarches, cold water soluble polysaccharides, gums and mixtures thereofin an amount sufficient to promote the suspension of said oocysts in theaqueous concentrate yet insufficient to impair the pourability orsprayability of said concentrate.
 2. An aqueous concentrate as claimedin claim 1 wherein said concentrate additionally contains traceingredients selected from the group consisting of minerals, vitamins,amino acids, carotenoid pigments, and mixtures thereof.
 3. An aqueousconcentrate as defined in claim 1 wherein the edible thickening agent ispresent in amounts ranging from about 0.1 to about 10% by weight of theaqueous concentrate.
 4. An aqueous concentrate as defined in claim 1,wherein the starches are selected from the group consisting of potatostarch, wheat starch and corn starch.
 5. An aqueous concentrate asdefined in claim 1, wherein the cold water soluble polysaccharides areselected from the group consisting of alkyl cellulose, carboxyalkylcellulose and hydroxyalkyl cellulose.
 6. An aqueous concentrate asdefined in claim 1, wherein the gums are selected from the groupconsisting of locust bean gum, guar gum and gum tragacanth.
 7. Anaqueous concentrate as defined in claim 5, wherein said cold watersoluble polysaccharide is carboxymethyl cellulose.
 8. A process for thepreparation of a pelleted feedstuff for poultry, wherein the pellets aresprayed with an aqueous concentrate as claimed in claim 11 to uniformlydistribute therein, per kilogram of feedstuff, from about 10 to about10,000 viable sporulated oocysts of at least one species of coccidia towhich poultry are susceptible, said sprayed feedstuff exhibiting a totalmoisture content of from about 6 to about 12 percent by weigh.